I havent been "stock" in so long, but you should be able to go: Hard Menu Button ---> Settings ---> Sound ---> Volume --->Once here, select the Media and Alarm sliders and slide them left all the way, then select the Ringtone slider and slide it all the way right. This should silence everything but the phone ringing for a call.

If this doesnt do what you want, then I recommend going to the Market and downloading ---> Quick Settings <---, this app will allow you to adjust multiple call settings as far as volume is concerned...

That may be a greta, and deceptively simple solution. Coing off a Blackberry Sound Setting were just so much easier and inuttitive with a "No sound" option in both the Phone Ringtones, Messaging, and Email categories.